With recent increased concern for an earth environment, better rate of fuel consumption (mileage) of an automobile is urgently required from energy save aspect. For realizing mileage of the automobile, decreasing mechanical loss of an engine is effective. Main mechanical loss is a piston drive loss resulted from slide resistance between a piston and an engine cylinder liner.
For decreasing the piston drive loss generally, a slide surface of the engine cylinder liner is lubricated by an oil film formed thereon. For formation of the oil film on the surface stably, pits becoming as oil storage are preferably formed.
Thus, the pits on the member are formed by forming cross-hatch simultaneous with cutting and grinding the member surface, or by forming convexes and concaves by shot peening.
However, conventional surface pit forming methods may cause following inconveniences. That is, in both of forming the cross-hatch and forming the convexes and concaves by shot peening, the pits formed have shallow depth. Also, in the pit formation, the pits unselectively formed make the whole surface coarse. As the result, performance of the surface as the slide surface is deteriorated. In addition, fine alumina powders used by the shot peening is hardly recycled.